Charged Au+/0/− species have been proposed as reaction centers for reduction and oxidation of organic molecules. The charged active sites of various Au+/0/− species are thought to play a key role in the oxidation of CO and styrene, the hydrogenation of ketones and aldehydes, as well as the reduction of CO2 and O2. Anionic, neutral and cationic Au species have all shown electrocatalytic activity towards CO2 reduction, CO oxidation and O2 reduction reactions. In order for rational catalyst design, active site composition must be identified. Knowing the active site composition then allows for the control of the active site, including charge state. We used atomically precise Au nanoclusters in specific charge states (q=−1, 0, +1) as electrochemical catalysts to study the role of charged active sites in electrochemical reactions.
One embodiment of the present invention showed Au25q nanoclusters providing charge state-dependent electrocatalytic activity for CO2 reduction, O2 reduction, and CO oxidation reactions in aqueous media. The small size of Au25q clusters leads to energy level quantization and the emergence of molecule-like charge state-dependent optical absorbance spectra. Au25q clusters possess an inherent negative charge and they carry a positive tetraoctylammonium (TOA) counter ion.